The present invention relates to a process for producing raw copper continuously in one stage by suspension smelting from sulfidic copper concentrates or ores containing impurities such as lead, antimony, bismuth and arsenic.
Most of the world's copper is still produced today by conventional processes which involve several different intermediate stages and products. The smelting of concentrate, or partly roasted concentrate, and slag-forming materials is performed in a basic smelting unit (reverberatory, electric, shaft or flash smelting furnace), whereafter the produced sulfidic copper matte is transferred to the converter for the production of blister copper. The last stage is normally a hot refining in order to regulate the oxygen and sulfur contents. The oxidic slag produced in the basic smelting unit is either rejected or treated further, depending on its valuable metal content. The converter slag is refined either separately or by returning it to the basic smelting unit. When treating unrefined concentrates by conventional processes it is clear, owing to the several intermediate products and the possibilities of varying each partial process independently, that impurities can easily be prevented from coming into the anode copper. This is so because in each partial process the sulfur and oxygen potentials of the system are different, and there by harmful secondary components can be removed selectively. On the other hand, if the batch process is used for the conversion, the values of the system change when the reactions proceed and this aids the formation of various intermediate products which can be removed when necessary.
The situation changes entirely when continuous processes are adopted, in which the produced metal is in an equilibrium with the various mattes and slags of the process or tends to reach such an equilibrium.
When discussing impurities present in copper concentrates, almost all elements except copper can be included among the impurities generally speaking. The number of components is actually smaller, since there are some which cannot thermodynamically dissolve to a harmful degree in the produced copper under the conditions prevailing in direct processes. Some of these are usually the strongly slag-forming components (e.g., Fe, Co, Zn, Cr, Ti, Ca, Si), which transfer to the silicate phase. On the other hand, it is desirable that some components accumulate in the raw copper (noble metals), and the removal of some (e.g. Ni) is relatively simple in the electrolytic process. Thus, some of the impurities usually counted as actually harmful are Pb, Sb, As, Bi.
When reviewing the patents relating to suspension smelting, it can be noted that the production of metal directly in the flash smelting furnace has long been under discussion. The process according to Finnish Pat. No. 22 694 constitutes an autogenic, basic suspension smelting process. Further, Finnish Pat. Nos. 45 866 and 47 380 describe how oxygen and sulfur pressures are used in controlled reaction shafts to create favorable conditions for the formation of white metal or even raw copper in the lower furnace. These patents deal with pure copper concentrates and only suggest the possibility of producing raw copper in a flash furnace without presenting more detailed examples.
When discussing other direct and/or continuous copper processes, they can be divided into two categories in regard to the oxidation of sulfides: (a) conversion-type processes in which most of the oxidation is performed in molten bath with the aid of either tuyeres or lancets and (b) suspension-type processes in which the oxidation reactions primarily occur in a suspension consisting of a finely-divided concentrate and reaction gas (combustion air).
The first example to be mentioned among the conversion-type processes is the Noranda process (Finnish Pat. No. 45 566 ), in which raw copper is produced from concentrates by a continuous process in one unit. The concentrates and slag-forming materials are added onto the molten bath and the oxidation takes place with the help of tuyeres under the melt surface. During continuous operation the melt comprises three layers which are only slingtly soluble in each other: slag, matte and raw copper. The slag (for further refining) and the sulfur-bearing raw copper are removed from the reactor. The smelting of unrefined concentrates is not discussed in the patent cited above, but according to an article concerning the same process (N.J. Themelis, G.C. McKerrow, P. Tarassoff, and G.D. Hollet: "The Noranda Process for Continuous Smelting and Converting of Copper Concentrates", 100th AIME Annual Meeting, New York, March 1-4, 197l), the removal of over 80% of the lead takes place by evaporation from the slag surface. The value is based on the lead contents of the slag and of the raw copper, given in the article, in which case in the concentrate Pb.about.1.2%.
The Worcra process can be mentioned as a second "conversion-type" process. It is described in, for example, U.S. Pat. No. 3 326 671 and in an article by H.K. Worner, J.O. Reynolds, B.S. Andrews and A.W.G. Collier: "Developments in WORCRA smelting-converting", Proceedings of an International Symposium, organized by the Institute of Mining and Metallurgy, London, Oct. 4-6, 1971. In this process the smelting of the concentrate and the slagging material takes place on the surface of the melt and the main oxidation by means of lancets from under the surface. The process operates according to the countercurrent principle to the effect that the waste slag and the raw copper are removed from opposite ends of the furnace. There are again very few references to unrefined concentrates. It is only noted in the article that an evaporation of 89% of the lead is possible (the lead content of the concentrate is 2.2%).
The Mitsubishi process can be mentioned as a third "conversion process". This process is described in, for example, Finnish Pat. Application 1397/73 and an article by T. Suzuki and T. Nagano: "Development of New Continuous Copper Smelting Process", Joint Meeting MMIJ - AIME, May 24-27, 1972, Tokyo. The system comprises three separate furnace units (smelting, slag-purification, and conversion) with a continuous flow of material between them. The actual burning of sulfur is performed with surface blast lancets, whereby raw copper is produced in the converter unit. In this process, as in the other conversion processes, there are three layers in the melt: slag, matte and raw copper. This is clearly indicated by the sulfur content of the raw copper produced (0.5 - 1.0% S), since it dissolves sulfur in an amount approaching equilibrium when it is produced by oxidation from molten sulfidic matte. As to impurities, it is mentioned in connection with the Mitsubishi process that when the copper content (.about.degree of oxidation) of the slag in the actual conversion furnace is raised, a Pb content within the range 0.2 - 0.5% is obtained for the produced raw copper, the lead content of the concentrate being 1.9 - 2.3%. Likewise, by raising the degree of oxidation it is possible to reduce the rates of other volatile impurities (As and Sb) in the raw copper as well. By this procedure the impurities can be removed in the dusts from the furnace.
When discussing the "suspension-type" processes for producing copper directly from concentrates, a few more processes can be mentioned in addition to those mentioned previously. Firstly, the Brittingham process (Finnish Pat. No. 45 463), in which an oxidation to the white-metal degree is performed in the reaction shaft, and the white metal is then further oxidized into raw copper. The purification of slag can be performed in the same unit in another part of the lower furnace. As in the conversion process, there are three melt phases: slag, matte and raw copper. No information has been given about the behavior of the impurities. Another possibility worth mentioning is the process introduced by J.C. Yannopoulos (U.S. Pat. No. 3, 674, 463), in which the copper matte produced during the first stage is further cycled in a molten state to be oxidized either in the same or a separate reaction shaft. By this procedure it is possible, according to the patent, to create metallic copper and a slag poor in valuable metals by maintaining a white-metal layer between the metal and slag phases. Neither in this patent is there mention of the behavior of the impurities.
The object of the present invention is thus to provide a process for the production of raw copper directly in the flash smelting furnace from impure sulfidic copper concentrate and/or ore by burning it with oxygen or oxygen enriched air.